antibiotic mechanism of action and resistance

1. Antibiotic resistanceAntibiotic resistance

2. • An antibiotic is a compound or substance that kills or
slows down the growth of microorganisms.

3. • The first antibiotic was penicillin, discovered accidentally
by Alexander Fleming when he observed that colonies of
the bacterium Staphylococcus aureus
could be destroyed by the
mold Penicillium notatum
in 1928.
• Today, over 100 different
antibiotics are available
to doctors to cure minor
discomforts as well as
life-threatening infections.

4. Sources of antibiotics
1-natural
mainly fungal sources.
2-semi-synthetic
Chemically altered natural compound.
3-synthetic
Chemically designed in the lab.

5. Classification
There are several classification schemes for
antibiotics based on:
• bacterial spectrum (narrow, broad ).
• route of administration (injectable ,oral or topical).
• type of activity (bactericidal or bacteriostatic).

6. But the most useful classification is based on chemical
structure. Compounds within a structural class will generally
show similar patterns of effectiveness and toxicity:
• Penicillins
are generally bactericidal-that is, they kill bacteria rather than inhibiting
growth. such as penicillin.
• Cephalosporins
are subgrouped into 1st, 2nd and 3rd generations. Each generation has a
broader spectrum of activity than the one before. such as cephalexin .
• Macrolides
macrolides got their name because they all have a macrocyclic lactone
chemical structure. such as erythromycin .

7. • Fluoroquinolones
are synthetic antibacterial agents. such as ciprofloxacin .
• Sulfonamides
are synthetic antimicrobial agents that contain the sulfonamide group. such
as Sulfamethoxazole .
• Tetracyclines
Tetracyclines got their name because they share a chemical structure that
has four rings. such as tetracycline.
• Aminoglycosides
are poorly absorbed through the gastrointestinal tract and are most
frequently administered IV. such as gentamicin.

8. How antibiotics work?
• Inhibition of Cell Wall Synthesis.
• Interfering with Protein Synthesis.
• Alteration of Cell Membrane.
• Inhibition of Nucleic Acid synthesis.
• Inhibiting the synthesis of essential metabolites

10. Antibiotic resistance problem
• Antibiotic resistance :is the ability of the
microorganism to withstand the effects of the drug.
• initially appeared in hospitals where antibiotics were
being used ,especially in military hospitals.

11. Types of resistance
• Intrinsic resistance
Inherent properties of the bacterium are responsible for preventing
antibiotic action. Penicillin G for example is unable to penetrate the
gram negative cell wall.
• Acquired resistance
Microorganisms generally acquired antibiotic resistance by genetic
changes.

12. Genetic basis of acquired resistance
1. Chromosomal mutation.
2. Plasmids.
3. Transposons.

13. Mechanisms of bacterial resistance to
drugs
1. Development of an altered drug target.
2. Decrease the concentration of the drug (Efflux pump).
3. Production of drug inactivating enzyme.
4. Synthesis of resistant metabolic pathway.
5. Failure to metabolize the drug.

15. • Antibiotic resistance can cause significant
danger and suffering for children and adults
who have common infections, once easily
treatable with antibiotics.
• If a microbe is resistant to many drugs,
treating the infections it causes, can become
difficult or even impossible.
• Someone with an infection that is resistant to
a certain medicine can pass that resistant
infection to another person. In this way, a
hard-to-treat illness can be spread from
person to person.
Medical importance of antibiotic
resistance

16. Factors predisposing to drug resistance
• Overuse of broad-spectrum antibiotics.
• incorrect diagnosis.
• improper use of antibiotics by patients.
• the use of antibiotics as livestock food additives for
growth promotion.